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![Tom Hromatka](/assets/img/avatar_default.png)
On systems with a large number of CPUs, running sysrq-<q> can cause watchdog timeouts. There are two slow sections of code in the sysrq-<q> path in timer_list.c. 1. print_active_timers() - This function is called by print_cpu() and contains a slow goto loop. On a machine with hundreds of CPUs, this loop took approximately 100ms for the first CPU in a NUMA node. (Subsequent CPUs in the same node ran much quicker.) The total time to print all of the CPUs is ultimately long enough to trigger the soft lockup watchdog. 2. print_tickdevice() - This function outputs a large amount of textual information. This function also took approximately 100ms per CPU. Since sysrq-<q> is not a performance critical path, there should be no harm in touching the nmi watchdog in both slow sections above. Touching it in just one location was insufficient on systems with hundreds of CPUs as occasional timeouts were still observed during testing. This issue was observed on an Oracle T7 machine with 128 CPUs, but I anticipate it may affect other systems with similarly large numbers of CPUs. Signed-off-by: Tom Hromatka <tom.hromatka@oracle.com> Reviewed-by: Rob Gardner <rob.gardner@oracle.com> Signed-off-by: John Stultz <john.stultz@linaro.org>
397 lines
9.4 KiB
C
397 lines
9.4 KiB
C
/*
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* kernel/time/timer_list.c
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*
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* List pending timers
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*
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* Copyright(C) 2006, Red Hat, Inc., Ingo Molnar
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*/
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#include <linux/proc_fs.h>
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#include <linux/module.h>
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#include <linux/spinlock.h>
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#include <linux/sched.h>
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#include <linux/seq_file.h>
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#include <linux/kallsyms.h>
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#include <linux/nmi.h>
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#include <linux/uaccess.h>
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#include "tick-internal.h"
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struct timer_list_iter {
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int cpu;
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bool second_pass;
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u64 now;
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};
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typedef void (*print_fn_t)(struct seq_file *m, unsigned int *classes);
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/*
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* This allows printing both to /proc/timer_list and
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* to the console (on SysRq-Q):
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*/
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__printf(2, 3)
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static void SEQ_printf(struct seq_file *m, const char *fmt, ...)
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{
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va_list args;
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va_start(args, fmt);
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if (m)
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seq_vprintf(m, fmt, args);
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else
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vprintk(fmt, args);
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va_end(args);
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}
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static void print_name_offset(struct seq_file *m, void *sym)
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{
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char symname[KSYM_NAME_LEN];
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if (lookup_symbol_name((unsigned long)sym, symname) < 0)
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SEQ_printf(m, "<%pK>", sym);
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else
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SEQ_printf(m, "%s", symname);
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}
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static void
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print_timer(struct seq_file *m, struct hrtimer *taddr, struct hrtimer *timer,
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int idx, u64 now)
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{
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SEQ_printf(m, " #%d: ", idx);
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print_name_offset(m, taddr);
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SEQ_printf(m, ", ");
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print_name_offset(m, timer->function);
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SEQ_printf(m, ", S:%02x", timer->state);
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SEQ_printf(m, "\n");
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SEQ_printf(m, " # expires at %Lu-%Lu nsecs [in %Ld to %Ld nsecs]\n",
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(unsigned long long)ktime_to_ns(hrtimer_get_softexpires(timer)),
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(unsigned long long)ktime_to_ns(hrtimer_get_expires(timer)),
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(long long)(ktime_to_ns(hrtimer_get_softexpires(timer)) - now),
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(long long)(ktime_to_ns(hrtimer_get_expires(timer)) - now));
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}
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static void
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print_active_timers(struct seq_file *m, struct hrtimer_clock_base *base,
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u64 now)
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{
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struct hrtimer *timer, tmp;
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unsigned long next = 0, i;
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struct timerqueue_node *curr;
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unsigned long flags;
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next_one:
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i = 0;
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touch_nmi_watchdog();
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raw_spin_lock_irqsave(&base->cpu_base->lock, flags);
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curr = timerqueue_getnext(&base->active);
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/*
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* Crude but we have to do this O(N*N) thing, because
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* we have to unlock the base when printing:
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*/
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while (curr && i < next) {
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curr = timerqueue_iterate_next(curr);
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i++;
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}
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if (curr) {
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timer = container_of(curr, struct hrtimer, node);
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tmp = *timer;
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raw_spin_unlock_irqrestore(&base->cpu_base->lock, flags);
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print_timer(m, timer, &tmp, i, now);
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next++;
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goto next_one;
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}
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raw_spin_unlock_irqrestore(&base->cpu_base->lock, flags);
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}
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static void
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print_base(struct seq_file *m, struct hrtimer_clock_base *base, u64 now)
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{
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SEQ_printf(m, " .base: %pK\n", base);
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SEQ_printf(m, " .index: %d\n", base->index);
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SEQ_printf(m, " .resolution: %u nsecs\n", hrtimer_resolution);
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SEQ_printf(m, " .get_time: ");
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print_name_offset(m, base->get_time);
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SEQ_printf(m, "\n");
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#ifdef CONFIG_HIGH_RES_TIMERS
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SEQ_printf(m, " .offset: %Lu nsecs\n",
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(unsigned long long) ktime_to_ns(base->offset));
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#endif
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SEQ_printf(m, "active timers:\n");
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print_active_timers(m, base, now + ktime_to_ns(base->offset));
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}
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static void print_cpu(struct seq_file *m, int cpu, u64 now)
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{
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struct hrtimer_cpu_base *cpu_base = &per_cpu(hrtimer_bases, cpu);
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int i;
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SEQ_printf(m, "cpu: %d\n", cpu);
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for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++) {
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SEQ_printf(m, " clock %d:\n", i);
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print_base(m, cpu_base->clock_base + i, now);
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}
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#define P(x) \
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SEQ_printf(m, " .%-15s: %Lu\n", #x, \
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(unsigned long long)(cpu_base->x))
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#define P_ns(x) \
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SEQ_printf(m, " .%-15s: %Lu nsecs\n", #x, \
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(unsigned long long)(ktime_to_ns(cpu_base->x)))
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#ifdef CONFIG_HIGH_RES_TIMERS
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P_ns(expires_next);
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P(hres_active);
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P(nr_events);
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P(nr_retries);
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P(nr_hangs);
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P(max_hang_time);
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#endif
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#undef P
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#undef P_ns
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#ifdef CONFIG_TICK_ONESHOT
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# define P(x) \
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SEQ_printf(m, " .%-15s: %Lu\n", #x, \
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(unsigned long long)(ts->x))
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# define P_ns(x) \
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SEQ_printf(m, " .%-15s: %Lu nsecs\n", #x, \
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(unsigned long long)(ktime_to_ns(ts->x)))
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{
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struct tick_sched *ts = tick_get_tick_sched(cpu);
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P(nohz_mode);
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P_ns(last_tick);
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P(tick_stopped);
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P(idle_jiffies);
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P(idle_calls);
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P(idle_sleeps);
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P_ns(idle_entrytime);
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P_ns(idle_waketime);
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P_ns(idle_exittime);
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P_ns(idle_sleeptime);
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P_ns(iowait_sleeptime);
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P(last_jiffies);
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P(next_timer);
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P_ns(idle_expires);
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SEQ_printf(m, "jiffies: %Lu\n",
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(unsigned long long)jiffies);
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}
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#endif
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#undef P
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#undef P_ns
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SEQ_printf(m, "\n");
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}
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#ifdef CONFIG_GENERIC_CLOCKEVENTS
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static void
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print_tickdevice(struct seq_file *m, struct tick_device *td, int cpu)
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{
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struct clock_event_device *dev = td->evtdev;
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touch_nmi_watchdog();
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SEQ_printf(m, "Tick Device: mode: %d\n", td->mode);
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if (cpu < 0)
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SEQ_printf(m, "Broadcast device\n");
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else
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SEQ_printf(m, "Per CPU device: %d\n", cpu);
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SEQ_printf(m, "Clock Event Device: ");
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if (!dev) {
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SEQ_printf(m, "<NULL>\n");
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return;
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}
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SEQ_printf(m, "%s\n", dev->name);
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SEQ_printf(m, " max_delta_ns: %llu\n",
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(unsigned long long) dev->max_delta_ns);
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SEQ_printf(m, " min_delta_ns: %llu\n",
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(unsigned long long) dev->min_delta_ns);
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SEQ_printf(m, " mult: %u\n", dev->mult);
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SEQ_printf(m, " shift: %u\n", dev->shift);
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SEQ_printf(m, " mode: %d\n", clockevent_get_state(dev));
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SEQ_printf(m, " next_event: %Ld nsecs\n",
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(unsigned long long) ktime_to_ns(dev->next_event));
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SEQ_printf(m, " set_next_event: ");
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print_name_offset(m, dev->set_next_event);
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SEQ_printf(m, "\n");
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if (dev->set_state_shutdown) {
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SEQ_printf(m, " shutdown: ");
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print_name_offset(m, dev->set_state_shutdown);
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SEQ_printf(m, "\n");
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}
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if (dev->set_state_periodic) {
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SEQ_printf(m, " periodic: ");
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print_name_offset(m, dev->set_state_periodic);
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SEQ_printf(m, "\n");
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}
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if (dev->set_state_oneshot) {
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SEQ_printf(m, " oneshot: ");
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print_name_offset(m, dev->set_state_oneshot);
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SEQ_printf(m, "\n");
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}
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if (dev->set_state_oneshot_stopped) {
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SEQ_printf(m, " oneshot stopped: ");
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print_name_offset(m, dev->set_state_oneshot_stopped);
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SEQ_printf(m, "\n");
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}
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if (dev->tick_resume) {
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SEQ_printf(m, " resume: ");
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print_name_offset(m, dev->tick_resume);
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SEQ_printf(m, "\n");
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}
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SEQ_printf(m, " event_handler: ");
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print_name_offset(m, dev->event_handler);
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SEQ_printf(m, "\n");
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SEQ_printf(m, " retries: %lu\n", dev->retries);
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SEQ_printf(m, "\n");
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}
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static void timer_list_show_tickdevices_header(struct seq_file *m)
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{
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#ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST
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print_tickdevice(m, tick_get_broadcast_device(), -1);
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SEQ_printf(m, "tick_broadcast_mask: %*pb\n",
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cpumask_pr_args(tick_get_broadcast_mask()));
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#ifdef CONFIG_TICK_ONESHOT
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SEQ_printf(m, "tick_broadcast_oneshot_mask: %*pb\n",
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cpumask_pr_args(tick_get_broadcast_oneshot_mask()));
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#endif
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SEQ_printf(m, "\n");
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#endif
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}
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#endif
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static inline void timer_list_header(struct seq_file *m, u64 now)
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{
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SEQ_printf(m, "Timer List Version: v0.8\n");
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SEQ_printf(m, "HRTIMER_MAX_CLOCK_BASES: %d\n", HRTIMER_MAX_CLOCK_BASES);
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SEQ_printf(m, "now at %Ld nsecs\n", (unsigned long long)now);
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SEQ_printf(m, "\n");
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}
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static int timer_list_show(struct seq_file *m, void *v)
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{
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struct timer_list_iter *iter = v;
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if (iter->cpu == -1 && !iter->second_pass)
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timer_list_header(m, iter->now);
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else if (!iter->second_pass)
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print_cpu(m, iter->cpu, iter->now);
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#ifdef CONFIG_GENERIC_CLOCKEVENTS
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else if (iter->cpu == -1 && iter->second_pass)
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timer_list_show_tickdevices_header(m);
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else
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print_tickdevice(m, tick_get_device(iter->cpu), iter->cpu);
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#endif
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return 0;
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}
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void sysrq_timer_list_show(void)
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{
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u64 now = ktime_to_ns(ktime_get());
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int cpu;
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timer_list_header(NULL, now);
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for_each_online_cpu(cpu)
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print_cpu(NULL, cpu, now);
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#ifdef CONFIG_GENERIC_CLOCKEVENTS
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timer_list_show_tickdevices_header(NULL);
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for_each_online_cpu(cpu)
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print_tickdevice(NULL, tick_get_device(cpu), cpu);
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#endif
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return;
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}
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static void *move_iter(struct timer_list_iter *iter, loff_t offset)
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{
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for (; offset; offset--) {
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iter->cpu = cpumask_next(iter->cpu, cpu_online_mask);
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if (iter->cpu >= nr_cpu_ids) {
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#ifdef CONFIG_GENERIC_CLOCKEVENTS
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if (!iter->second_pass) {
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iter->cpu = -1;
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iter->second_pass = true;
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} else
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return NULL;
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#else
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return NULL;
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#endif
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}
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}
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return iter;
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}
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static void *timer_list_start(struct seq_file *file, loff_t *offset)
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{
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struct timer_list_iter *iter = file->private;
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if (!*offset)
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iter->now = ktime_to_ns(ktime_get());
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iter->cpu = -1;
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iter->second_pass = false;
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return move_iter(iter, *offset);
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}
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static void *timer_list_next(struct seq_file *file, void *v, loff_t *offset)
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{
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struct timer_list_iter *iter = file->private;
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++*offset;
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return move_iter(iter, 1);
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}
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static void timer_list_stop(struct seq_file *seq, void *v)
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{
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}
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static const struct seq_operations timer_list_sops = {
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.start = timer_list_start,
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.next = timer_list_next,
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.stop = timer_list_stop,
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.show = timer_list_show,
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};
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static int timer_list_open(struct inode *inode, struct file *filp)
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{
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return seq_open_private(filp, &timer_list_sops,
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sizeof(struct timer_list_iter));
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}
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static const struct file_operations timer_list_fops = {
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.open = timer_list_open,
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.read = seq_read,
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.llseek = seq_lseek,
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.release = seq_release_private,
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};
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static int __init init_timer_list_procfs(void)
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{
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struct proc_dir_entry *pe;
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pe = proc_create("timer_list", 0444, NULL, &timer_list_fops);
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if (!pe)
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return -ENOMEM;
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return 0;
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}
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__initcall(init_timer_list_procfs);
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